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2003

Iowa State University

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Articles 1 - 30 of 38

Full-Text Articles in Engineering

Prediction Of Dopant Ionization Energies In Silicon: The Importance Of Strain, A. Rockett, Duane D. Johnson, S. V. Khare, B. R. Tuttle Dec 2003

Prediction Of Dopant Ionization Energies In Silicon: The Importance Of Strain, A. Rockett, Duane D. Johnson, S. V. Khare, B. R. Tuttle

Duane D. Johnson

Based on a hydrogenic state and strain changes upon defect charging, we propose a simple, parameter-free model that agrees well with the observed group III and V monovalent-impurity ionization energies in Si, revealing the importance of such strain effects. Changes in lattice strain upon defect charging are obtained via superposition and elasticity theory using atomic relaxations from density functional theory.

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Analysis Of Core Buckling Defects In Sheet Metal Coil Processing, P.M. Lin, Jonathan A. Wickert Nov 2003

Analysis Of Core Buckling Defects In Sheet Metal Coil Processing, P.M. Lin, Jonathan A. Wickert

Jonathan A. Wickert

The elastic stability of a wound coil comprising a central core and many layers of sheet metal is modeled and analyzed. A common failure mode resulting from unfavorable internal stresses—called v-buckling—is characterized by a section of the core buckling inward, possibly with several nearby sheet metal layers. In the present study, the core is modeled as a thin cylinder that is subjected to (i) the uniform external pressure generated by the coil's wound-in stresses and (ii) a nonuniform elastic foundation around its circumference that represents core-coil contact or loss thereof. The model and an iterative numerical technique are used to …

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Estimations Of Ammonia And Hydrogen Sulfide Fluxes From Cattle Feedlot Surfaces In Texas High Plains, Bok-Haeng Baek, Jacek A. Koziel, Jarett P. Spinhirne, David B. Parker, Nolan A. Cole Oct 2003

Estimations Of Ammonia And Hydrogen Sulfide Fluxes From Cattle Feedlot Surfaces In Texas High Plains, Bok-Haeng Baek, Jacek A. Koziel, Jarett P. Spinhirne, David B. Parker, Nolan A. Cole

Jacek A. Koziel

A dynamic flow-through chamber system and continuous analyzers were used for on-site measurements of ammonia-nitrogen (NH 3 -N) and hydrogen sulfide-sulfur (H 2 S-S) fluxes from commercial feedlot surfaces in northwestern Texas during two week period in the summer of 2002. Ambient air and air inside chamber temperatures, and manure pack temperature were measured continuously. Manure pack moisture content, pH, and TKN were measured daily to characterize its correlation with NH 3 -N fluxes. The preliminary average NH 3 -N flux from the feedlot surface for the entire measurement period was 1,669 ± 1,212 NH 3 -N µ g/m 2 …

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Generation And Calibration Of Standard Gas Mixtures For Volatile Fatty Acids Using Permeation Tubes And Solid Phase Microextraction, Jacek A. Koziel, Jarett P. Spinhirne Oct 2003

Generation And Calibration Of Standard Gas Mixtures For Volatile Fatty Acids Using Permeation Tubes And Solid Phase Microextraction, Jacek A. Koziel, Jarett P. Spinhirne

Jacek A. Koziel

Volatile fatty acids (VFAs) are major components of odors associated with agricultural operations and livestock housing, solid waste processing and disposal, and industrial and municipal wastewater collection and treatment systems. Emissions estimation and assessment of odor control methods depend on reliable air sampling and analysis methods for VFAs. The objective of this research was to develop and test a method for continuous and reliable generation of standard gas mixtures for VFAs based on permeation tubes. Standard gas mixtures for acetic, propionic, isobutyric, butyric, isovaleric, valeric, and hexanoic acids were generated with permeation tubes and monitored for a 100-day period. The …

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Ammonia Concentrations In Poultry Broiler Production Units Treated With Liquid Alum, K. A. Armstrong, Robert T. Burns, F. R. Walker, L. R. Wilhelm, D. Raj Raman Oct 2003

Ammonia Concentrations In Poultry Broiler Production Units Treated With Liquid Alum, K. A. Armstrong, Robert T. Burns, F. R. Walker, L. R. Wilhelm, D. Raj Raman

D. Raj Raman

High ammonia concentrations in commercial broiler production houses can result in poor bird performance, lower feed conversion ratios, and higher mortalities. Growers have traditionally controlled in-house ammonia levels by increasing ventilation. During cold weather, increased ventilation rates result in higher heating energy requirements. Granular alum (aluminum sulfate, Al2(SO4)3 · 14H2O) has been successfully used as a litter amendment to reduce ammonia volatilization from litter inside broiler production houses. In this study, liquid aluminum sulfate was investigated as a litter amendment for ammonia suppression in four commercial poultry-broiler units. This project investigates four treatment levels of liquid alum in four adjacent …

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Measurements Of The Longitudinal Wave Speed In Thin Materials Using A Wideband Pvdf Transducer, Kwang Yul Kim, Wei Zou, Stephen D. Holland, Wolfgang Sachse Sep 2003

Measurements Of The Longitudinal Wave Speed In Thin Materials Using A Wideband Pvdf Transducer, Kwang Yul Kim, Wei Zou, Stephen D. Holland, Wolfgang Sachse

Stephen D. Holland

A flat transducer was constructed, using a 9-mm-thick PVDF (polyvinylidene fluoride) film for generation and detection of high-frequency ultrasonic waves, and used for measurements of the phase velocity of longitudinal waves traveling along the thickness direction in a very thin material. The transducer has a useful wideband frequency characteristic extending from 10 MHz to over 150 MHz. Measurements of the phase velocity of the longitudinal waves are carried out using a 0.212-mm-thick glass slide and a 0.102-mm-thick stainless-steel shim, using water as a coupling medium. The thickness limit for this measurement appears to be approximately 20 mm. The phase velocity …

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Laboratory Measurements Of Differential Diffusion In A Diffusively Stable, Turbulent Flow, P. Ryan Jackson, Chris R. Rehmann Aug 2003

Laboratory Measurements Of Differential Diffusion In A Diffusively Stable, Turbulent Flow, P. Ryan Jackson, Chris R. Rehmann

Chris R. Rehmann

Laboratory experiments were performed to determine the conditions under which differential diffusion occurs and to evaluate its effect on the mixing efficiency. Diffusively stable profiles of temperature and salinity were stirred steadily by horizontally oscillating vertical rods. The two-component stratification ensures that both scalars experience the same stratification and forcing, or Richardson and Reynolds numbers. The eddy diffusivities KT and KS, for temperature and salinity, were estimated by fitting theoretical solutions of diffusion equations to measured profiles, and the mixing efficiency was computed as the ratio of the potential energy change during a stirring interval to the work done in …

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Competition Between Ferromagnetism And Antiferromagnetism In Fept, G. Brown, B. Kraczek, A. Janotti, T. C. Schulthess, G. M. Stocks, Duane D. Johnson Aug 2003

Competition Between Ferromagnetism And Antiferromagnetism In Fept, G. Brown, B. Kraczek, A. Janotti, T. C. Schulthess, G. M. Stocks, Duane D. Johnson

Duane D. Johnson

Ni/Fe/Co/Cu(100) films were epitaxially grown and investigated by photoemission electron microscopy. The magnetic correlation of the Ni and Co films was investigated by element-specific domain images. We found that the Ni magnetization exhibits a continuous rotation in the spin reorientation transition (SRT) region and that the Ni SRT thickness oscillates with the Fe film thickness.

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Simulated Assembly Of Nanostructured Organic/Inorganic Networks, Monica H. Lamm, Ting Chen, Sharon C. Glotzer Aug 2003

Simulated Assembly Of Nanostructured Organic/Inorganic Networks, Monica H. Lamm, Ting Chen, Sharon C. Glotzer

Monica H. Lamm

We perform-lattice Monte Carlo simulations to study nanostructured networks formed by linking organically functionalized inorganic nanoscale building blocks. We develop a minimal lattice model of an octafunctional nanoscale building block (NBB) by representing the inorganic core with a rigid cube and the organic linkers with "bead-spring" chains. Using this model, we explore the effect of linker length on network properties including porosity, spatial distribution of NBBs, and extent of cross-linking during assembly. We compare our results with recent experimental data on networks of octafunctional polyhedral oligomeric silsesquioxane (POSS) cubes.

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Release And Transport Of Bacteria And Nutrients From Livestock Manure Applied To Pastureland, Michelle L. Soupir Jul 2003

Release And Transport Of Bacteria And Nutrients From Livestock Manure Applied To Pastureland, Michelle L. Soupir

Michelle L. Soupir

Transport of fecal bacteria and nutrients from point and nonpoint sources to surface water bodies is of significant concern in Virginia and the United States. In Virginia, 4,320 river miles are impaired for one or more beneficial use and 72% of the streams are impaired due to pathogen indicators (VDEQ, 2002). Land applications of manure from confined animal systems and by direct deposit by grazing animals are both major sources of fecal bacteria and nutrients in runoff. Therefore, an understanding of the overland transport mechanisms for fecal bacteria and nutrients is very important for the development of best management practices …

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Vibration Of Flex Circuits In Hard Disk Drives, Jonathan A. Wickert Jul 2003

Vibration Of Flex Circuits In Hard Disk Drives, Jonathan A. Wickert

Jonathan A. Wickert

A flex circuit connects the stationary electronic components in a hard disk drive to the rotating arm that carries the read/write heads and positions them above data tracks on the disk. Flex circuits are conventionally formed as a laminate of polyimide substrate, adhesive, and copper conductors. Deformation of a flex circuit is discussed in the context of the following stages: the initial unstressed shape, configurations in which stresses set and relax in response to elevated temperature, equilibrium, and small amplitude vibration. The model involves displacements of the flex circuit in the directions tangent and normal to the local equilibrium shape, …

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Properties Of Corn Masa Processing Byproducts, Kurt A. Rosentrater Jul 2003

Properties Of Corn Masa Processing Byproducts, Kurt A. Rosentrater

Kurt A. Rosentrater

The production of corn masa-based products in the U.S. has been increasing over the last several years, and as a result, so has the quantity of waste materials generated from this industry. These byproduct materials may have potential for value-added processing and utilization, which are options that hold the promise of economic benefits for masa processors and decreased potential pollution for the environment. Fundamental to any byproduct development, however, is a full characterization of the processing residue, because physical and nutritional properties are necessary for the proper design of processing operations and applications. Vital physical properties include moisture content, water …

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Using Efficient Software Architecture For Computer-Based Training Programs To Promote International Development, Kurt A. Rosentrater, Kari Pape Rosentrater Jul 2003

Using Efficient Software Architecture For Computer-Based Training Programs To Promote International Development, Kurt A. Rosentrater, Kari Pape Rosentrater

Kurt A. Rosentrater

Many international agencies offer volunteer services to improve agricultural knowledge and infrastructure in developing countries. Although effective, these efforts are severely constrained by limited funding and personnel, and can only address a fraction of current global educational needs. Computer-based training programs, either in the form of CD-ROM-based or Internet-based incarnations, hold the promise of removing many of the obstacles that currently confront international volunteer efforts. The art of web programming has drastically accelerated in recent years, both in terms of capacity as well as complexity. One reason for this is that advanced software has been developed to simplify and speed …

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Assessment Of Moisture Control And Additives For Odor Reduction From Open-Lot Feedyard Surfaces, Jocelyn D. Buchanan, David B. Parker, Marty B. Rhoades, Jacek A. Koziel, William J. Rogers Jul 2003

Assessment Of Moisture Control And Additives For Odor Reduction From Open-Lot Feedyard Surfaces, Jocelyn D. Buchanan, David B. Parker, Marty B. Rhoades, Jacek A. Koziel, William J. Rogers

Jacek A. Koziel

Amendments for reducing odor from open-lot beef cattle feedyards were evaluated in the laboratory. Manure was placed in small Tupperware® containers. Water and amendments were added to the manure surface and the containers were attached to a vacuum pump that continually passed 2.5 L/min of carbon-filtered air over the surface. Eleven different amendments were tested, at two different concentrations, in a series of five experiments. Odor samples were collected 3 times during a 10-day period in each experiment and were analyzed by trained panelists for detection threshold (DT), intensity and hedonic tone. None of the amendments showed any overwhelming evidence …

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Background Odors In Tedlar® Bags Used For Cafo Odor Sampling, David B. Parker, Marty B. Rhoades, Jacek A. Koziel, Jarett Spinhirne Jul 2003

Background Odors In Tedlar® Bags Used For Cafo Odor Sampling, David B. Parker, Marty B. Rhoades, Jacek A. Koziel, Jarett Spinhirne

Jacek A. Koziel

Tedlar® film is manufactured in a wet solvent process and continues to emit organic compounds after manufacturing. Tedlar® bags are used for odor sampling at concentrated animal feeding operations (CAFOs). Odor regulations for CAFOs vary widely, but maximum detection thresholds (DTs) of 2 to 15 have been proposed downwind of feeding operations. Results at the WTAMU Olfactometry Laboratory have shown that both commercially available Tedlar® bags and homemade Tedlar® bags have a detectable background odor (DTs of 20 to 60 typical) even following standard protocols for purging. Purging the bags before sampling was not effective in reducing DTs to acceptable …

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Estimation Of Ammonia And Hydrogen Sulfide Emissions From Cattle Feedlots In Texas, Bok-Haeng Baek, Jacek A. Koziel, Jarett P. Spinhirne, David B. Parker, Nolan A. Cole Jul 2003

Estimation Of Ammonia And Hydrogen Sulfide Emissions From Cattle Feedlots In Texas, Bok-Haeng Baek, Jacek A. Koziel, Jarett P. Spinhirne, David B. Parker, Nolan A. Cole

Jacek A. Koziel

A dynamic flow-through chamber system and continuous analyzers were used for on-site measurements of ammonia-nitrogen (NH 3 -N) and hydrogen sulfide-sulfur (H 2 S-S) fluxes from commercial feedlot surfaces in northwestern Texas during two week period in the summer of 2002. Manure pack moisture content, pH, and TKN were measured daily to characterize its relation with NH 3 -N fluxes. The preliminary average NH 3 -N and H 2 S-S flux from the feedlot surface were 1,669 ± 1,212 NH 3 -N µ g/m 2 /min and 1.884 ± 1.497 H 2 S-S µ g S/m 2 /min. Manure pack …

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Bacteria Release And Transport From Livestock Manure Applied To Pastureland, Michelle L. Soupir, H. E. Saled Mostaghimi, Elizabeth F. Alphin Jul 2003

Bacteria Release And Transport From Livestock Manure Applied To Pastureland, Michelle L. Soupir, H. E. Saled Mostaghimi, Elizabeth F. Alphin

Michelle L. Soupir

A comparative field investigation was conducted on release and transport of bacteria from plots treated with cowpies, turkey litter, and liquid dairy manure. Rainfall conditions were simulated and runoff samples were collected to determine concentrations of E. coli, FC, and enterococcus present in runoff. The turkey treatment had the highest percentage of source bacteria released by rainfall, ranging from 1.3% for enterococcus to 14.5% for FC. The cowpie follows with percentages ranging from 0.3 to 0.6%. Runoff samples collected from the transport plots treated with cowpies averaged 137,000 cfu/100 ml for E. coli and over 165,000 cfu/100 ml for FC …

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Soil Moisture Estimation From Remotely Sensed Hyperspectral Data, Amy L. Kaleita, Lei F. Tian, Haibo Yao Jul 2003

Soil Moisture Estimation From Remotely Sensed Hyperspectral Data, Amy L. Kaleita, Lei F. Tian, Haibo Yao

Amy L. Kaleita

A methodology for mapping surface soil moisture content across an agricultural field from optical remote sensing and ground sampling is developed. This study uses both ground-based and remotely sensed spectral measurements of soil reflectance in visible and near-infrared wavelengths and concurrent measurements of volumetric soil moisture within the top 6 cm. After determining appropriate wavelengths for soil moisture estimation from spectral reflectance, a cokriging scheme was used to generate soil moisture maps. Results indicate that combining reflectance and ground measurements can yield more detailed maps of soil moisture than ground measurement alone.

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Soil Moisture Estimation From Remotely Sensed Hyperspectral Data, Amy L. Kaleita, Lei Tian, Haibo Yao Jul 2003

Soil Moisture Estimation From Remotely Sensed Hyperspectral Data, Amy L. Kaleita, Lei Tian, Haibo Yao

Amy L. Kaleita

A methodology for mapping surface soil moisture content across an agricultural field from optical remote sensing and ground sampling is developed. This study uses both ground-based and remotely sensed spectral measurements of soil reflectance in visible and near-infrared wavelengths and concurrent measurements of volumetric soil moisture within the top 6 cm. After determining appropriate wavelengths for soil moisture estimation from spectral reflectance, a cokriging scheme was used to generate soil moisture maps. Results indicate that combining reflectance and ground measurements can yield more detailed maps of soil moisture than ground measurement alone.

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Modeling Of Sediment Trapping In A Vegetative Filter Accounting For Two-Dimensional Overland Flow, Matthew J. Helmers, Dean E. Eisenhauer, Thomas G. Franti, Michael G. Dosskey Jul 2003

Modeling Of Sediment Trapping In A Vegetative Filter Accounting For Two-Dimensional Overland Flow, Matthew J. Helmers, Dean E. Eisenhauer, Thomas G. Franti, Michael G. Dosskey

Matthew J. Helmers

Vegetative filters (VF) are used to remove sediment and other pollutants from overland flow. When modeling the hydrology of VF it is often assumed that overland flow is planar but our research indicates that it can be two-dimensional with converging and diverging pathways. Our hypothesis is that flow convergence will negatively influence the sediment trapping capability of VF. The objectives were to develop a two-dimensional modeling approach for estimating sediment trapping in VF and to investigate the impact of converging overland flow on sediment trapping by VF. In this study, the performance of a VF that has field-scale flow path …

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Development Of A Controller Area Network Based Handheld Data Acquisition System For Identity Preservation, Matthew J. Darr, Jason Kellam Ward, Timothy S. Stombaugh, Michael D. Montross Jul 2003

Development Of A Controller Area Network Based Handheld Data Acquisition System For Identity Preservation, Matthew J. Darr, Jason Kellam Ward, Timothy S. Stombaugh, Michael D. Montross

Matthew J. Darr

The development of a diverse, modular and portable system to accurately measure and record field operations is required to effectively bring identity preservation of crops to all farms and farmers. A demonstration system has been built based on a worldwide standard communications protocol and was evaluated for its ability to efficiently measure a variety of field operations and management practices. The CAN Bus 2.0B communication protocol was used to record GPS location data, ground speed and simulated spraying system data. This data was compiled and stored in a form that was compatible with multiple software programs for the purposes of …

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Odor Characterization At Open-Lot Beef Cattle Feedyards Using Triangular Forced Choice Olfactometry, David B. Parker, Marty B. Rhoades, Brent W. Auvermann, Jacek A. Koziel Jul 2003

Odor Characterization At Open-Lot Beef Cattle Feedyards Using Triangular Forced Choice Olfactometry, David B. Parker, Marty B. Rhoades, Brent W. Auvermann, Jacek A. Koziel

Jacek A. Koziel

Odor samples were collected two to four times per month over a one-year period in 2002-2003 at three large open-lot beef cattle feedyards in the Texas panhandle. Samples were collected in 10 L Tedlar bags using a vacuum chamber upwind of the feedyard, downwind of the pens, and downwind of the runoff storage pond. Samples were analyzed in the odor lab for detection threshold (DT) using triangular forced choice olfactometry with trained human odor panelists. Full-strength odor samples were also analyzed for intensity and hedonic tone. Weather data was collected on-site at each of the feedyards for correlation to odor …

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Characterization Of Volatile Organic Compounds In Bovine Breath Using Solid-Phase Microextraction And Gas Chromatography-Mass Spectrometry, Jacek A. Koziel, Jarett P. Spinhirne, Norbert K. Chirase Jul 2003

Characterization Of Volatile Organic Compounds In Bovine Breath Using Solid-Phase Microextraction And Gas Chromatography-Mass Spectrometry, Jacek A. Koziel, Jarett P. Spinhirne, Norbert K. Chirase

Jacek A. Koziel

A face mask sampling device, DVB/Carboxen/PDMS 50/30 µ m solid phase microextraction (SPME) fibers, and a gas chromatograph with a mass spectrometer detector (GC-MS) were used for sampling and analysis of volatile organic compounds (VOCs) in bovine breath. Breath of 3 morbid steers with respiratory tract infections and 3 healthy steers were sampled 7 times in 19 days for 15 min at each sampling. A total of 21 VOCs were detected, many of them for the first time in cattle breath. Preliminary statistical analyses using Chi-square Test on the frequency of detection of each VOC in each group was performed. …

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Предсказание Термодинамики И Упорядочения В Металлических Сплавах Из Первых Принципов, Николай Заркевич Jun 2003

Предсказание Термодинамики И Упорядочения В Металлических Сплавах Из Первых Принципов, Николай Заркевич

Nikolai A. Zarkevich

Кластерные разложения по взаимодействиям все чаще используются для много- масштабного моделирования, сочетающего расчёты электронной структуры из первых принципов и методы Монте-Карло для предсказания термодинамических свойств сплавов. Кластерное разложение – это разложение по базису геометрических объектов (кластеров) на решётке и эффективных межатомных взаимодействий. Кластерное разложение может быть математически точным и бесконечным, но практично только в усечённом конечном базисе. Однако до сих пор процедура усечения базиса не была строго определена и не гарантировала надёжный результат. Мы предлагаем метод оптимального усечения базиса геометрических кластеров, который ведёт к надёжным предсказаниям термодинамики. Далее для примера мы проводим количественный расчёт термодинамических свойств ГЦК сплава Ni3V и …

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Assessment Of Introduction To Engineering And Problem-Solving Course, Joni E. Spurlin, Jerome P. Lavelle, Mary Clare Robbins, Sarah A. Rajala Jun 2003

Assessment Of Introduction To Engineering And Problem-Solving Course, Joni E. Spurlin, Jerome P. Lavelle, Mary Clare Robbins, Sarah A. Rajala

Sarah A. Rajala

At North Carolina State University, the freshmen’s first course in engineering is E101, Introduction to Engineering and Problem-Solving. It is offered each fall to over 1,100 first year engineering students. In an effort to continuously improve the course, we put into place a plan to assess the course's learning outcomes. Assessment data collected in fall 2001 and fall 2002 through surveys, rubrics, and class assignments were evaluated to determine how well students met learning outcomes related to communication, teamwork, and problem-solving. This paper presents the assessment methods used in this course and provides examples of how the assessment findings were …

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Reply To “Comment On ‘Classical Density Functional Theory Of Freezing In Simple Fluids: Numerically Induced False Solutions’ ”, M. Valera, F. J. Pinski, Duane D. Johnson May 2003

Reply To “Comment On ‘Classical Density Functional Theory Of Freezing In Simple Fluids: Numerically Induced False Solutions’ ”, M. Valera, F. J. Pinski, Duane D. Johnson

Duane D. Johnson

Recently we solved, via discrete numerical grids, the Ramakrishna-Yossouff density-functional theory equations for the freezing transition and obtained an intricate phase diagram of hard-sphere mixtures. Even though such methods provide more variational freedom than basis-set methods, we found that the thermodynamic quantities were sensitive to the spacing of numerical grids employed and observed numerically induced false minima. Dasgupta and Valls have commented that these false minima were due to our use of k-space methods and, hence, their early works based on a fully r-space approach are qualitatively correct, despite also being sensitive to the mesh granularity. Here, we clarify the …

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Predicted Hcp Ag-Al Metastable Phase Diagram, Equilibrium Ground States, And Precipitate Structure, Nikolai A. Zarkevich, Duane D. Johnson Feb 2003

Predicted Hcp Ag-Al Metastable Phase Diagram, Equilibrium Ground States, And Precipitate Structure, Nikolai A. Zarkevich, Duane D. Johnson

Nikolai A. Zarkevich

Formation energies of a number of hcp-based Ag-Al structures are obtained from ab initio electronic-structure calculations and used within a cluster expansion approach to construct an effective alloy Hamiltonian. Formation energies are found to be inherently asymmetric versus composition, providing an incipient tendency for precipitation in Al-rich alloy. Both ground-state search and Monte Carlo simulations based on the cluster expansion are used to determine the metastable hcp Ag-Al phase diagram. A new equilibrium hcp AgAl ground state is predicted and zero-energy domain boundary defects are found. From thermodynamic results, we discuss the precipitate structure and composition in Al-rich Al-Ag alloys …

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Absolute Orientation-Dependent Anisotropic Tin(111) Island Step Energies And Stiffnesses From Shape Fluctuation Analyses, S. Kodambaka, S. V. Khare, V. Petrova, Duane D. Johnson, I. Petrov, J. E. Greene Jan 2003

Absolute Orientation-Dependent Anisotropic Tin(111) Island Step Energies And Stiffnesses From Shape Fluctuation Analyses, S. Kodambaka, S. V. Khare, V. Petrova, Duane D. Johnson, I. Petrov, J. E. Greene

Duane D. Johnson

In situ high-temperature (1165–1248 K) scanning-tunneling microscopy was used to measure temporal fluctuations about the anisotropic equilibrium shape of two-dimensional TiN(111) adatom and vacancy islands on atomically smooth TiN(111) terraces. The equilibrium island shape was found to be a truncated hexagon bounded by alternating 〈110〉 steps, which form [100] and [110] nanofacets with the terrace. Relative step energies β as a function of step orientation φ were obtained from the inverse Legendre transformation of the equilibrium island shape to within an orientation-independent scale factor λ, the equilibrium chemical potential of the island per unit TiN area. We find that for …

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Three-Dimensional Landau Theory For Multivariant Stress-Induced Martensitic Phase Transformations. Iii. Alternative Potentials, Critical Nuclei, Kink Solutions, And Dislocation Theory, Valery I. Levitas, Dean L. Preston, Dong Wook Lee Jan 2003

Three-Dimensional Landau Theory For Multivariant Stress-Induced Martensitic Phase Transformations. Iii. Alternative Potentials, Critical Nuclei, Kink Solutions, And Dislocation Theory, Valery I. Levitas, Dean L. Preston, Dong Wook Lee

Valery I. Levitas

In part III of this paper, alternative Landau potentials for the description of stress-and temperature-induced martensitic phase transformations under arbitrary three-dimensional loading are obtained. These alternative potentials include a sixth-degree (2-4-6) polynomial in Cartesian order parameters and a potential in hyperspherical order parameters. Each satisfies all conditions for the correct description of experiments. The unique features of the potentials are pointed out and a detailed comparison of the potentials is made for NiAl alloy. Analytic solutions of the one-dimensional time-independent Ginzburg-Landau equations for the 2-3-4 and 2-4-6 potentials for a constant-stress tensor and invariant-plane strain are obtained and compared. Solutions …

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Kinematic Effects Of Differential Transport On Mixing Efficiency In A Diffusively Stable, Turbulent Flow, P. Ryan Jackson, Chris R. Rehmann Jan 2003

Kinematic Effects Of Differential Transport On Mixing Efficiency In A Diffusively Stable, Turbulent Flow, P. Ryan Jackson, Chris R. Rehmann

Chris R. Rehmann

If temperature and salinity are mixed at different rates, the mixing efficiencies in flows with the same stratification and forcing can vary if the contributions of temperature and salinity to the density differ. Two models are used to examine the effect of differential transport of salt and heat on the mixing efficiency. The first model assumes constant eddy diffusivities for heat and salt and examines the effect of the density ratio Rρ = αΔT/βΔS and the diffusivity ratio d = KS/KT on the mixing efficiency. The model predicts that the effect of differential transport can be as large as that …

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